Essentially, the Stereo Vitalizer Jack offers the SPL magic at an accessible price. • The Bass knob works on the bottom end of your mix. Turning it to the left produces a more round, warm, soft effect, while moving it to the right produces a tighter, harder sound.

• The Mid-Hi Tune knob sets the starting frequency of a broad-band shelving filter, allowing you to select where within the mid-frequency range the Vitalizer starts processing. While the unit has a range of between 1kHz and 20kHz, most of the action will be in the 3.5kHz to 8kHz region.

• The Process knob controls the amount of bass and mid-range intensity. Basically, it gives you either more or less of the effect you've set with the Bass and Mid-Hi Tune knobs.

• The Brilliance control works on higher frequencies, without, somehow, actually boosting them in the way that many exciters do. The result is a more natural sound, less tiring on the ears, which adds clarity to the mix. To check out the effect of the Brilliance knob on its own, turn the Process knob full left. You'll find the Bass and Mid-Hi Tune controls now have no effect.

• The Stereo Expander uses a pretty straightforward technique (feeding opposite-phase signals from one channel to the other) to take the stereo image beyond the boundary of your speakers. It works well, making the finer details of your mix even more apparent.